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Old World Monkeys Developed Facial Features to Discourage Hybridization, Says Study

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A recently published scientific study explains that the faces of Old World monkeys have evolved in order to prevent members of this species from crossbreeding. The report, which appeared this week in the academic journal Nature Communications, explains that the evolution of the monkeys’ facial feature is a direct result of the specie’s goal to “strengthen reproductive isolation between populations.” The study was undertaken by a team of researchers from two prestigious academic institutions: NYU in the United States and Exeter University in the United Kingdom.

This means that Old World monkeys specifically evolved to look different from other species that lived in the same geographical area – or at least nearby. The author of the study, James Higham, an assistant professor from the Department of Anthropology at New York University, explained the evolutionary mechanism in more detail. According to Higham, “Evolution produces adaptations that help animals thrive in a particular environment, and over time these adaptations lead to the evolution of new species. A key question is what mechanisms keep closely related species that overlap geographically from inter-breeding, so that they are maintained as separate species?”

According to the results of the research, it’s all about differentiating between members of the same species thanks to their distinct facial features. Some of the features used as markers, in telling Old World monkeys apart from members of other primate species, include various markings on their faces, patches of eyebrow hair in different colors, tufts of hair around the ears, spots on the monkeys’ noses, patches around their mouths, and others.

The scientists photographed and then undertook an analysis of about 22 types of guenon monkeys. Also known under the scientific name of cercopithecini, this group of monkeys appeared and developed in the Central and West African forests. The study looked at their facial features, which were plotted out via imaging and then compared. The analysis revealed that, in time, the markings and features of each species became more and more substantially differentiated. According to the same study, the species which lived closer together and spent more time in each other’s proximity were that much more likely to stand apart.

The study was led by William Allen, a researcher who has since moved from the Department of Anthropology at NYU to the similar department at England’s University of Hull. Allen explained that the monkeys look so distinct today because they naturally selected specimens with “visual signals that discourage hybridization. This is perhaps the strongest evidence to date for a role for visual signals in the key evolutionary processes by which species are formed and maintained, and it is particularly exciting that we have found it in part of our own lineage.”